Peripheral filtering lens

ABSTRACT

A filter or lens for a star tracking telescope includes a clear center portion and an attenuating peripheral portion where the peripheral portion attenuation of off-axis images is nonidentical through any radial line extending from a center of the filter or lens to a circumference edge of the filter or lens for passing on-axis images with high signal to noise ratios and for attenuating off-axis images for attenuating but not completely blocking the off-axis images, which telescope with such a filter or lens is well suited for improved star tracking systems, and well suited for reducing off-axis glare in handheld optical apparatus such as binoculars, telescopes, cameras, and eyeglasses.

STATEMENT OF GOVERNMENT INTEREST

The invention was made with Government support under contract No.FA8802-00-C-0001 by the Department of the Air Force. The Government hascertain rights in the invention.

REFERENCE TO RELATED APPLICATION

The present application is related to applicant's copending applicationentitled Peripheral Filtering Star Tracker Telescope Ser. No.11/525,645, filed Sep. 20, 2006.

The present application is related to applicant's copending applicationentitled Peripheral Filtering Eyeglass and Camera Optical Systems SerNo.12/386,282, filed Apr. 16, 2009, by the same inventors.

FIELD OF THE INVENTION

The invention relates to the field of optical imaging systems. Moreparticularly, the invention relates to filters and lenses such as thosefor use in star tracking telescopes, which lenses have image peripheralfiltering characterized as peripherally attenuating radiallynonidentical filtering.

BACKGROUND OF THE INVENTION

Star tracking telescopes have long been used in spacecraft fordetermining the location of a spacecraft by reference to imaged stars. Atypical tracking system includes a star tracking telescope and can becontrolled, moved, and rotated so at to keep the boresight axis pointingat a tracked star so as to keep an image of the star along boresight ina center of a field of view. The field of view may also include imagesof nearby stars. Images of nearby stars can further enhance on-boardpositioning systems to determine when the tracked star is the desiredstar for tracking. Images of the nearby stars can be used to determine astar pattern and hence function as a reference pattern of a cluster ofstars where one of the stars within the cluster is to be tracked. Oncethe desired tracking star has been located and the telescope is moved tomaintain tracking of that tracked star, images of the nearby stars maystill disadvantageously remain within the field of view.

An image of nearby stars, within the field of view, passes throughfront-end filters and lenses in a peripheral portion of the front-endfilters and lenses while an image of the tracked star enters through thecenter of the front-end filters or lenses as a tracked star that istracked. When tracking a tracked star, it is desirable to maintain ahigh signal to noise ratio especially where the image of the trackedstar is a faint image. However, off-axis nearby star images as well assunlight can disadvantageously inject signal noise into the telescope.

Various prior means have been used to minimize unwanted nearby star andsun tracker noise. Existing tracking telescopes have used elongatedcylindrical tubular shades with internal baffling to reduce the amountof off-axis noise. The longer the elongated cylindrical tubular baffledshade, the more that off-axis image noise is reduced. Such shades havebeen further modified with a shade extension also having a matingtubular cross section but cut so that the shade extension functionprovides increased shading from above noise images with no shading frombelow noise shading so as to provide a nonlinear off-axis shadingprofile. In both cases, the prior shades disadvantageously extended theover all physical length of the telescopes that are intended to fitswithin a predetermined and dimensionally limited existing spacecrafttracking system. The baffling of the prior shades also have variousbaffle angles so as to vary the amount of off-axis noise reaching theback end optical sensors. The various baffle angles have a limitedangular design, and hence, disadvantageously have a limited amount ofnoise rejection.

In the photography art, shades have also long been used to limit theamount of off-axis glare from affecting the quality of photographicpictures. Some lenses have been equipped with attenuating lenses toreduce the amount of light received in high glare environments. However,such a shade also decreases the amount of light, and hence, decreasesthe image quality of the desired image to be photographed. This issimilar to common sunglasses where it is desirable to reduce glare fromall directions, including on-axis images. Cameras have used concentriclenses and filters where a center portion of the lens is clear and anouter portion is matted so as to fuzz without attenuation the peripheryof the resulting photographic image so as to provide an artistic styledphotograph where the center portion remains clear.

Handheld binoculars and telescopes have also been equipped with shadesto reduce off-axis glares for improved image quality. Handheldbinoculars and telescopes have been equipped with opaque filters toreduce image brightness across the entire field of view. Generally,handheld binoculars and telescopes do not use attenuating filters asthese optical devices seek, in the main, to magnify a distal object.

Some optical filters and lenses have used fixed or variably sizedshutters and sized irises to restrict the field of view, as is wellknown. In the case of costume eyeglasses, such as those used by childrenat play, a center portion of a lens is an open aperture while theremaining portion of the lens completely blocks image reception. Inother types of costume eyeglasses, young adults have used decorativelenses where ornamental flakes are bonded to the lenses to provide aprovocative appearance where the flakes obscure peripheral vision. Manypeople, especially the aged, have problems with night glare and haveused sunglasses while driving a night. However, sunglasses dim on-axisvision that reduces visual acuity along an intended line-of-sightincreasing the problems of poor night perception. Star trackingtelescopes, and common handheld optical apparatus, such as handheldcameras, binoculars, eyeglasses, and telescopes suffer from the problemof injecting bright off-axis noise into the image quality of on-axisimages or suffer from the problem of blocking needed peripheral visionand image reception. These and other disadvantages are solved or reducedusing the invention.

SUMMARY OF THE INVENTION

An object of the invention is to provide an optical system attenuatingperipheral images.

Another object of the invention is to provide an optical tracking systemusing a telescope for attenuating peripheral images.

Yet another object of the invention is to provide optical systems usingperipheral image attenuating lenses and filters that can be easilymanufactured.

Still another object of the invention is to provide optical systemshaving peripheral image attenuating lenses and filters having identicalradial image attenuation in a peripheral portion of the lenses andfilters.

A further object of the invention is to provide optical systems havingperipheral image attenuating lenses and filters having nonidenticalradial image attenuation in a peripheral portion of the lenses andfilters.

Yet a further object of the invention is to provide eyeglasses forreducing nighttime glare for improved nighttime driving.

Still a further object of the invention is to provide cameras forreducing photographic glare for improved photographic quality.

The present invention is directed to optical systems having front-endlenses or filters that peripherally attenuate incoming off-axis imagesso as to preserve the fidelity of on-axis images in the center of afield of view while retraining a portion of the off-axis image.Peripheral off-axis images are attenuated so as to preserve the fidelityof forward vision and on-axis image reception while also receivingattenuated peripheral off-axis images. The purpose is to avoiddistortion and maintain high image fidelity of the forward centeredregion of the field of view while diminishing by attenuation moderatelyundesirable off-axis images that are not completely blocked so as topreserve some peripheral vision in the periphery of the field of view.This center preservation and periphery attenuation has severalapplications and can be realized by various manufacturing methods.

The invention is characterized in three aspects. A first aspect isprimarily a direct application for minimizing star tracker noise. In thepreferred form, the first aspect adapts a gradient optical filter to aconventional star tracker telescope. A second aspect of the invention isdirected to various manufacturing processes or making differing types ofperiphery attenuated front-end lenses and filters. A third aspect of theinvention is the application of periphery attenuating lenses and filtersto common commercial optical apparatuses such as eyeglasses and cameras.

In the first aspect, an image tracking system, such as a star trackingsystem, uses a star tracker telescope. The star tracking telescopetracks a foreign body by moving an optical boresight axis that remainsin alignment and in the direction of that tracked body where thetracking system uses periphery attenuating filters or lenses. In thepreferred form, a star tracker telescope is pointed directly toward atracked star for providing a high intensity and unattenuated image ofthat tracked star. The tracked star image passes through the center of afront-end filter for receiving a high fidelity image of that trackedstar so as to maintain maximum signal strength for star tracking.Off-axis star images are received through the periphery of the front-endfilter. The off-axis images are attenuated in signal strength so thatthe off-axis star images can still be seen but without substantial glareinterference to the tracked star image, so that, reference to theoff-axis star can be maintained without degrading the image of theon-axis star image that is tracked for improved star-trackingperformance. The proposed filtering is preferably by gradient or uniformfiltering that has zero attenuation in the center clear portion of thefilter but has equicircumferential radial attenuation in a peripheryportion of the filter where the amount of attenuation has identicalattenuation profiles along any identical radially extending line fromthe center and through the periphery portion of the filter.

In the second aspect of the invention, the periphery attenuating filtersor lenses have nonidentical attenuation profiles along any identicalradially extending line from the center through the periphery portion ofthe lenses or filters. In an exemplar form, the periphery portion iscoated with a solid reflecting coating for blocking all transmissionsthrough selected portions of the periphery portion. The coating isconfigured during manufacture in the shape of triangular wedgesequiangularly disposed in the periphery portion. The wedges radiallyextend from the outer circumference and point towards the center of thefilter that still retains a center clear transmissive portion providingan inner portion of transparency and an outer portion of reflection.These reflecting triangular wedges provide effective gradientattenuation but can be easily realized through manufacture of solidreflective coatings.

In the third aspect of the invention, the periphery attenuating filtersor lenses are applied to nontracking optical systems, such as commoneyeglasses and photographic cameras, generally having the purpose ofreducing periphery glare. In the case of eyeglasses, the lenses of theeyeglasses have a periphery attenuating portion so as to reduceperiphery glare that may, for example, be distracting for nighttimeautomobile drivers, yet preserve enough of the periphery visions forvisual perception similar to sunglass intensity attenuation. Thesesunglasses preserve the forward center view for maintaining full forwardvision acuity for improved safety during driving by reducing the commonaffliction of night blindness and while reducing glare. In the case ofphotographic cameras, the attenuating periphery portion of a front-endfilter or lenses prevents side lighting from producing glare thatadversely affects the image quality in the center of the field of viewfrom improved accurate and artistic photography.

The periphery attenuation front-end filters and lenses can be used toenhance image tracking, human visual perception, and photographicquality. These and other advantages will become more apparent from thefollowing detailed description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a star tracker telescope with a gradient filter

FIG. 2 is a diagram of an annular absorption filter

FIG. 3 is a diagram of a triangular annular absorption filter.

FIG. 4 is a diagram of annular lens eyeglasses.

FIG. 5 is a diagram of reduced glare optics.

FIG. 6 is a diagram of an edge-attenuating lens.

FIG. 7 is a diagram of a patterned attenuating lens.

FIG. 8 is a diagram of a reduced glare camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention is described with reference to thefigures using reference designations as shown in the figures. Referringto FIG. 1, a star tracker telescope includes an optical sensor 10, abandpass filter 12, an optical lens 14, a tubular shade 15, and anannular filter 16 for focusing received images upon a focal plane 17.The tubular shade 15 may include baffles 18. A bright off-axis starimage 20 and a dim on-axis star image 22 provide optical images. Theimages pass through the annular filter 16, the focal plane 17, andoptical lens 14 for activating the optical sensor 10 that provideselectronic images of the bright off-axis star image 20 and the dimon-axis star image 22 for star tracking. The bright off-axis image 20could be an image of the sun or a distal bright star. The dim on-axisstar image 22 could be a dim remote star that is to be tracked.

The bright star off-axis image 20 passes through the tubular shade 15along an attenuated bright star optical path 30 to the focal plane 14,lens 12, and sensor 10. The dim star image 22 passes along a dim staroptical path 32 to the focal plane 14, lens 12, and sensor 10. Thebright star off-axis image 20 also passes through the tubular shade 15along an absorbed bright star optical path 34 where a portion of thebright star off-axis image is absorbed by the baffles 18. The brightstar off-axis image 20 also passes through and is reflected by thetubular shade 15 along a reflected bright star optical path 36, to thefocal plane 14, lens 12, and sensor 10.

The annular filter 16 includes a clear circular center portion 40passing the dim on-axis star image 22 along the dim star optical path32. The clear circular center portion 40 is completely transmissive anddoes not attenuate the signal strength of dim on-axis star image 22. Theannular filter 16 further includes an attenuating annular portion 42that attenuates the signal strength of the bright star off-axis image 20along the attenuated bright star optical path 30, absorbed bright staroptical path 34, and the reflected bright star optical path 36. Hence,an attenuating annular portion 42 of the annular filter 16 serves toattenuate the signal strength, but does not completely block the signalof the bright star off-axis image 20. Concurrently, the clear circularcenter portion 40 of the annular filter 16 serves to passes the dimon-axis star image 22. In this manner, the optical sensor 10 receivesthe dim on-axis star image 22 with maximum signal strength whilereceiving the bright star off-axis image 20 with reduced signalstrength.

Referring to FIGS. 1 and 2, and more particularly to FIG. 2, the annularfilter 16 is an annular absorption filter having the center clearportion 40 and the attenuating annular portion 42. The clear portion 40is centered in the filter 16 and is defined by a radius R. Theattenuating annular portion 42 is an outer portion defined by thecircumference of the clear portion 40. The outer circumference of thefilter 16 is defined by a diameter D. In one form of the invention, theattenuating annular portion 42 is defined by an identical attenuationprofile that is equal and identical along any radial line extending fromthe center of the filter 16 to the circumference of the filter 16. Morepreferably, the attenuation profile of the attenuating annular portion42 could be a uniform profile providing uniform attenuation along anyradial line where the attenuation is equal at all points along allradial lines through the portion 42. The attenuation profile could be agradient profile providing linearly increasing or decreasing amounts ofattenuation at points along all radial lines through the portion 42.

Referring to FIGS. 1 through 3, and more particularly to FIG. 3, anotherpreferred form of the invention is a triangular annular filter that isalso an attenuating annular filter having a nonidentical amount ofattenuation along the radial lines. In this form, the annular filter 16has triangular density portions 48 that extend from an inner R diameter44 to an outer circumference having an outer D diameter 46. Thetriangular portions 48 are a plurality of like triangular portions beingisosceles triangles or wedges having tips at the inner R diameter 44 anda base running substantially in coincident alignment with thecircumference having an outer D diameter of the filter 16. Thetriangular portions 48 can provide uniform or gradient attenuation. Oneparticular case of uniform attenuation of the triangular portions 48 isreflection providing complete attenuation. In operation, the triangularportions 48 collectively function to attenuate the bright off-axis starimages even when the triangular portions 48 are reflective. Uncoatedclear optics is disposed in the center while the triangular portions 48are disposed on the periphery of the filter 16. The triangular portions48 could be easily made by reflective manufacturing masks producingsilver mirrored surfaces.

In operation, the annular filters 16 may take various forms, such aswith identical or nonidentical radial attenuation profiles, but at aminimum has an annular outer portion 42 for attenuating the off-axisimages and a clear center portion for passing on-axis images. As afurther enhancement, and at a minimum, the center portion could alsohave some attenuation filter so long as it is distinct from and lessattenuation of the outer annular portion passing an attenuated remainderof the off-axis image. This dual attenuation feature is well suited forstar tracking telescopes, but could also be applied to other opticalapparatus, such as personal eyeglasses, binoculars, telescopes, andcameras.

Referring to FIG. 4, a pair of annular lenses are disposed in eyeglassesincluding an eyeglasses frame 50 supporting a right eyeglass lens 51 aand a left eyeglass lens 51 b. Each of the lenses 51 a and 51 g includean annular attenuating portion 52 for attenuating off-axis images and aclear center portion 54. The lenses 51 a and 51 b need not be circular.The lenses 51 a and 52 b may be for example, substantially rectangularin perimeter shape but have two distinct portions, the center portion 54that may be, for example, oval in shape, and an outer portion 54 thatmay have an inner oval edge and an outer rectangular edge. The centerportion 54 and annular attenuating portion 52 would have respectivedifferences in the respective amounts of attenuation. In the preferredform, the inner portion is transparent and the outer portion is opaque.

Referring to FIG. 5, a human eyeball 56 functions to receive both anoff-axis image 57 and on-axis image 59 for human perception using aretina focal surface 58 in the eyeball 56. The off-axis image 57 may bea glaring image and the on-axis image 59 may be a target image. Anexemplar eyeglass lens 60 includes a clear circular center portion 61through which passes the on-axis image along an on-axis target opticalpath 63, and includes a lens attenuating annular portion 64 throughwhich passes the off-axis image along an off-axis glaring optical path62. The lens 60 may be a prescription lens for providing both correctivevision and off-axis attenuation.

Referring to FIG. 6, an edge-attenuating lens has opposing side-edgeattenuating portions 65 and a clear center portion 66 for attenuatingleft and right off-axis images while not attenuating top and bottomoff-axis images. The edge-attenuating lens can have various otherpossible preferred forms, such as attenuating up and bottom off-axisimages. The edge-attenuating lens is characterized as having anonidentical attenuation profile along all radial lines extending fromthe center of the lens 64.

Referring to FIG. 7, a patterned attenuating lens 67 is configured withattenuating squares 68 that may be partially transmissive or completelyreflective. The patterned attenuating lens 67 is also characterized ashaving a nonidentical attenuation profile along all radial linesextending from the center of the lens 67. Various shapes andprescriptions can be used in many possible variants so long as an outerportion of the lens 67 attenuates in some measure more than a centerportion of the lens having a distinctly differing lesser amount ofattenuation, such as transparency or significantly reduced attenuation.For example, the lens could be part of prescription sunglasses having amuch more darker and opaque outer portion for increased off-axisattenuation as compared to less on-axis attenuation for definingvariants of annular filtering. The eyeglasses 50 could be used byautomobile drivers suffering from poor night vision. Unwanted off-axisimages tend to glare and degrade perception of the on-axis images. Theeyeglasses 50 would not attenuate on-axis red tail lights of cars in adriver's immediate front, but would attenuate off-axis periphery lightfrom headlights of on-coming traffic for improve driving safety, yetremain enough of the off-axis image for visual periphery perception andsafety.

Referring to FIG. 8, annular filtering can be applied to many otheroptical apparatus, such as a glare reduction camera 69 including animage sensor 70 which may be for example, a CCD electronic sensor orphotographic film. The glare reduction camera 69 would include a cameraannular filter 72 and a camera lens 74. The annular filter 72 wouldpreferably include a clear portion 61 for passing by transparency anon-axis image 59 along the on-axis optical path 63 for photographing theon-axis image 59. The annular filter 72 would further include an outerannular portion 64 for attenuating along the off-axis optical path 62the off-axis image 57. In so doing, the photographic image would reducelight intensity of the off-axis image thereby reducing unwanted glareduring photography while retaining a clear and bright photograph of theon-axis image. The application of the off-axis periphery attenuation canequally be applied generally to other optical apparatus includingmechanical handheld binoculars and telescopes.

The present invention is directed to an optical apparatus including afront-end lens or filter that distinctly attenuates an off-axis imagemore than an on-axis image. In one form, an optical filter is mounted onthe light shade with a clear transparent center portion in the centerand with a gradient or uniform attenuating outer portions that wouldattenuate the stray light effects for improved star tracking of anon-axis image passing through the center portion. There are manyadvantages to reducing but not completely eliminating glint, glare,stray, or bright periphery light in various optical systems.Peripheral-attenuating optical systems are applicable to star trackers,as well as Earth sensors, horizon sensors, sun sensors, opticaltelescopes, and infrared telescopes. Peripheral-attenuating opticalfilters and lenses can in general be applied to any optical systems,including commercial cameras, eyeglasses, binoculars, hobby telescopes,and video systems. Those skilled in the art can make enhancements,improvements, and modifications to the invention, and theseenhancements, improvements, and modifications may nonetheless fallwithin the spirit and scope of the following claims.

1. A filter for use in an optical system comprising: an electronicphotographic imaging sensor for imaging an on-axis image of an on-axisobject and an off-axis image of an off-axis object, the optical systemhaving one or more first optical elements and an optically opposed andphysically remote focal plane end; the filter being one of the firstoptical elements; an inner portion of the filter passing the on-axisimage, an outer portion of the filter for attenuating the off-axis imageof the off-axis object, the off-axis image of the off-axis object beinga peripheral image passing through the filter's outer portion, thefilter's outer portion having a nonidentical attenuation profile alongpoints along any radial line extending from a center in the innerportion of the filter and through the filter's outer portion, theoff-axis image and the on-axis image being imaged concurrently by theoptical system, the off-axis image being incompletely blocked whenpassing through a selected portion of the filter's outer portion, andinformation sufficient to reproduce a photograph of the on-axis imagebeing available from the imaging sensor.
 2. The filter of claim 1wherein, the inner portion is a transparent portion passing the on-axisimage with zero attenuation.
 3. The filter of claim 2 wherein, thenonidentical attenuation has a varying profile indicating varyingamounts of attenuation at points along any radial line extending fromthe center of the filter and through the outer portion.
 4. The filter ofclaim 1 wherein, the filter is a circular filter.
 5. The filter of claim1 wherein the filter is a circular filter, the inner portion is acircular inner portion, and the outer portion is an annular portion. 6.The filter of claim 1 wherein, the outer portion is a peripheral annularportion, the outer portion comprises the selected portion being aplurality of equiangularly spaced opaque triangular portions, the outerportion comprises a plurality of equiangularly spaced transparenttriangular portions, and the outer portion being an annular portionabout the inner portion.
 7. The filter of claim 1 wherein, the filter isused in a telescope.
 8. The filter of claim 1 wherein, the filter isused in a star tracker telescope.
 9. The filter of claim 1 wherein, thefilter is used in a passive optical apparatus comprising a frame forsupporting the filter.
 10. The filter of claim 1 wherein, the filter isa lens.
 11. The system of claim 1 wherein, the on-axis object is a star,and the off-axis object is a star.
 12. The filter of claim 1 wherein theattenuation of the filter is selected to enable a photographic image ofthe image sensor to show a light source of interest and a relativelybright light source when the light source of interest would haveotherwise been obscured by the bright light source.
 13. The filter ofclaim 12 further comprising: an enclosed optical path extending betweenthe filter and the image sensor, and baffles affixed to an inner surfaceof the enclosed optical path.
 14. The filter of claim 13 wherein aphotographic image of the on-axis object is available from the imagesensor.
 15. A system for electronically imaging an on-axis image of anon-axis object and an off-axis image of an off-axis object, the systemcomprising, an electronic photographic imaging sensor, the imagingsystem having one or more first optical elements and an opticallyopposed and physically remote focal plane end, a filter being one of thefirst optical elements and having an inner portion and an outer portion,the outer portion blocking and passing the off-axis image of theoff-axis object, the off-axis image of the off-axis object being aperipheral image passing through portions of the outer portion, theouter portion having a nonidentical attenuation profile along pointsalong any radial line extending from a center in an inner portion of thefilter and through the outer portion, the outer portion comprises aplurality of equiangularly spaced blocking triangular portions disposedabout the inner portion, the triangular portion being reflective andblocking, an imager for imaging the off-axis image and the on-axisimage, the attenuation profile serving to attenuate the off-axis imagemore than the on-axis image as imaged by the imager, and informationsufficient to reproduce a photograph of the on-axis image beingavailable from the imaging sensor.
 16. The system of claim 15 wherein,the inner portion is transparent, and the outer portion is blocking. 17.The system of claim 15 wherein, the triangular portion extends to aperiphery of the filter.
 18. The system of claim 15 wherein, the innerportion and outer portion are sized relative to each other and to theactive system for imaging both the on-axis image and the off-axis image.